Method of forming contact openings

ABSTRACT

The invention includes etching and contact opening forming methods. In one implementation, a plasma etching method includes providing a bottom powered plasma chamber that includes a plasma generating electrode powerable at different first and second frequencies, with the first frequency being lower than the second frequency. A substrate is positioned over the electrode. A plasma is generated over the substrate with the electrode from a first applied power at the first frequency and a second applied power at the second frequency. A ratio of the first applied power to the second applied power is from 0 to 0.25 or at least 6.0. Material is etched from the substrate with the plasma.

TECHNICAL FIELD

The present invention relates to plasma etching methods and to contactopening forming methods.

BACKGROUND OF THE INVENTION

In the fabricating of integrated circuitry, different elevationconductive and/or semiconductive layers are commonly separated byinsulative layers. Electrical connections are commonly made betweendifferent elevation devices by forming contact openings through aninsulating layer prior to forming the higher elevation devices. Suchopenings are typically formed through a masking layer using ananisotropic plasma etching technique. One particular class of tools fordoing so is known as a bottom powered, dual frequency etch system. Ithas been found in certain instances when operating such systems in themanner recommended by the manufacturer that electrical characteristicsof the fabricated circuitry were being shifted or changed in undesirablemanners. One discovered adverse effect was a decrease in the fieldthreshold voltage. This is a measurement of the voltage required to formundesired parasitic field effect transistors across field isolation onthe substrate. It is typically desirable that this voltage be as high aspossible to avoid the formation of such parasitic devices.

An exemplary plasma etch apparatus and data from semiconductorsprocessed according to the prior art are shown in FIGS. 1-3. Referringto FIG. 1, an exemplary bottom powered dual frequency plasma etchapparatus is shown. Apparatus 10 includes a bottom powered electrode 12and a top unpowered, grounded electrode 14. Electrode 12 has dualfrequency power sources of 2 and 27 MHz respectively. An exemplaryapparatus 10 is the Exelan system produced by LAM Research Corporationof Freemont, Calif., which is a bottom powered dual frequency etchsystem. During plasma etch, this system is powered simultaneously at 2MHz and 27 MHz with substantially balanced or equal powers. For example,these powers are typically run at greater than 1000 watts each, with apower ratio from 0.6 to 1.67 of the 2 MHz frequency to the 27 MHzfrequency (2 MHz:27 MHz).

Semiconductor substrates processed under these conditions can developlow field threshold voltages, as well as other adverse effects such asinadequate refresh times. FIGS. 2 and 3 illustrate the low fieldthreshold values of semiconductor substrates processed in accordancewith these prior art methods. Referring to FIG. 2, at high total power(3050 watts) and low frequency ratio of 0.65, the field thresholdvoltage was 5.92. Likewise, as illustrated in FIG. 3, at a total powerof approximately 3050 watts and a high frequency ratio of about 1.6, thefield threshold voltage was 5.52. It is preferred to maintain the totalpower as high as possible to increase etch rates, thereby processingsubstrates in a more rapid manner.

While the invention was motivated by addressing the above issues andchallenges, it is, of course, in no way so limited. This invention isonly limited by the accompanying claims as literally worded andappropriately interpreted in accordance with the doctrine ofequivalents.

SUMMARY OF THE INVENTION

The invention includes etching and contact opening forming methods. Inone implementation, a plasma etching method includes providing a bottompowered plasma chamber that includes a plasma generating electrodepowerable at different first and second frequencies, with the firstfrequency being lower than the second frequency. A substrate ispositioned over the electrode. A plasma is generated over the substratewith the electrode from a first applied power at the first frequency anda second applied power at the second frequency. A ratio of the firstapplied power to the second applied power is from 0 to 0.25 or at least6.0. Material is etched from the substrate with the plasma.

In one implementation, a method of forming contact openings includesproviding a bottom powered plasma chamber comprising a plasma generatingelectrode powerable at different first and second frequencies, with thefirst frequency being lower than the second frequency. A substrate ispositioned over the electrode. The substrate includes an insulativelayer received over conductive or semiconductive material. A patternedmasking layer having openings therein for defining contact openings isreceived over the insulative layer. The insulative layer includes anoutermost portion and an innermost portion proximate the conductive orsemiconductive material. Contact openings are formed through theinsulative layer to the conductive or semiconductive material using thepatterned masking layer by first removing the outermost portioneffective to expose the innermost portion. Then, the innermost portionis plasma etched effective to expose the conductive or semiconductivematerial. Plasma may or may not be used in removing the outermostportion. Regardless, the plasma used to etch the innermost portion isgenerated with the electrode from a first applied power at the firstfrequency and second applied power at the second frequency. A ratio ofthe first applied power to the second applied power is from 0 to 0.25 orat least 6.0.

Other aspects and implementations are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic depiction of a prior art bottom powered, dualfrequency plasma chamber usable in accordance with aspects of theinvention.

FIG. 2 is a graph of data obtained from a semiconductor substrateprocessed according to prior art methods.

FIG. 3 is a graph of data obtained from a-semiconductor substrateprocessed according to prior art methods.

FIG. 4 is a diagrammatic cross-sectional view of a substrate in processin accordance with an aspect of the invention.

FIG. 5 is a view of the FIG. 4 substrate at a processing stagesubsequent to that of FIG. 4.

FIG. 6 is a view of the FIG. 5 substrate at a processing stagesubsequent to that of FIG. 5.

FIG. 7 is a graph of data obtained from a semiconductor substrateprocessed in accordance with aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

An exemplary plasma etching method in accordance with aspects of thepresent invention is described with reference to FIGS. 4-7. Referring toFIG. 4, a substrate 20 includes conductive or semiconductive material 24having insulative material 26 thereover. In the illustrated embodiment,substrate 20 includes a patterned masking layer 32 formed overinsulative material 26 to be used as a mask in etching material 26.

The term “substrate” refers to any supporting structure, including, butnot limited to the conductive and semiconductive materials describedherein. Semiconductive material can include any construction comprisingsemiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). Material 24 can include semiconductive materials, forexample polysilicon. In one implementation, material 24 can includeconductive materials, for example metals such as copper, other elementalmetals and alloys, or conductive metal compounds. An exemplary preferredmaterial 26 comprises SiO₂, for example borophosphosilicate glass.Insulative material 26 can also include multiple insulative materialsand/or layers.

In one implementation, insulative material 26 can be considered ashaving an innermost portion 28 proximate material 24 and having anoutermost portion 30. In the illustrated embodiment, innermost portion28 and outermost portion 30 of insulative material 26 can comprise theentire thickness of insulative material 26. In an exemplary aspect, athickness of outermost portion 30 is at least five times the thicknessof innermost portion 28. In another exemplary aspect, the thickness ofoutermost portion 30 is at least nine times the thickness of innermostportion 28. A specific example thickness for innermost portion 28 isfrom 1,000 Å to 2,000 Å, with that for outermost portion 30 being from18,000 Å to 19,000 Å.

An example material for masking layer 32 is photoresist. Any othermasking material is contemplated, whether existing or yet-to-bedeveloped. Multiple materials and layers are also contemplated for layer32. In FIGS. 4-6, an exemplary method of forming contact openings isshown. Masking layer 32 has an opening 33 formed therein for defining acontact opening in material 26.

Substrate 20 is positioned over a plasma generating electrode of abottom powered plasma chamber, for example as shown in FIG. 1. TheExelan dual frequency bottom powered etching system described above isan exemplary bottom powered plasma chamber. Regardless, the plasmagenerating electrode is powerable at different first and secondfrequencies, with the first frequency being lower than the secondfrequency. By way of example only, the first frequency can be 2 MHz andthe second frequency can be 27 MHz as with the Exelan system.

Referring to FIG. 5, outermost portion 30 has been removed effective toexpose innermost portion 28. Outermost portion 30 may be removed througha number of techniques. In one implementation, outermost portion 30 maybe removed by plasma etching. Plasma may be generated over substrate 20with the electrode from a first applied power at the first frequency anda second applied power at the second frequency. The first applied powerand the second applied power can each be greater than 1000 watts duringthe removing, and a sum of the first applied power and the secondapplied power can be at least 3000 watts. In particular aspects, thefirst applied power can be 0 or greater than 0. In an exemplary aspect,when removing outermost portion 30, a ratio of the first applied powerto the second applied power is from 0.26 to 5.9; from 0.6 to 1.67;and/or from 0 to 0.25 or at least 6.0. Further, etching might beconducted without plasma generation. Regardless, an exemplary etchingchemistry for etching borophosphosilicate glass includes C₄F₈, O₂ andAr.

Referring to FIG. 6, innermost portion 28 has been plasma etched to formcontact opening 34. Plasma is generated over substrate 20 with theelectrode from a first applied power at the first frequency and a secondapplied power at the second frequency. When etching innermost portion28, the ratio of the first applied power to the second applied power isfrom 0 to 0.25 or at least 6.0. The first applied power can be 0 orgreater than 0. The first applied power and the second applied power arepreferably each greater than 1000 watts during the etching, and a sum ofthe first applied power and the second applied power is preferably atleast 3000 watts.

In an exemplary aspect, the removing of outermost portion 30 removes atleast five times the material as does the etching of innermost portion28. In another aspect, the removing of outermost portion 30 removes atleast nine times the material as does the etching of innermost portion28. In one aspect, outermost portion 30 is removed at a higher rate thaninnermost portion 28 is etched.

In one implementation, the outermost portion and the innermost portionare both plasma etched. A sum of the applied powers utilized to etch theinnermost portion can be less than a sum of the applied powers used toetch in the outermost portion. The applied powers used to etch theoutermost portion, for example, can each be greater than 1000 wattsand/or have a sum total greater of at least 3000 watts. In an exemplaryaspect, one of the applied powers utilized to etch the innermost portionis equal to one of the applied powers utilized to etch the outermostportion.

Referring to FIG. 7, the field threshold voltage of exemplary substrate20 having contact openings 34 formed therein is illustrated. As isshown, the field threshold voltage is approximately seven as compared tothe approximate five of the prior art.

The above exemplary described embodiment was with respect to exemplaryaspects of methods of forming contact openings. However, the inventionis in no way so limited. Rather, the invention in its broadest aspectcan be considered as a plasma etching method wherein a substrate ispositioned over a bottom powered plasma generating electrode of a bottompowered plasma chamber. The bottom powered electrode is powerable atdifferent first and second frequencies, with the first frequency beinglower than the second frequency. Plasma is generated over the substratewith the electrode from a first applied power at the first frequency anda second applied power at the second frequency. A ratio of the firstapplied power to the second applied power is from 0 to 0.25, or at least6.0. Material is etched from the substrate with the plasma. Accordingly,the invention is contemplated as just so literally stated andindependent of whether contact openings or other openings are beingformed relative to a substrate. Preferred attributes with respect to theplasma etching are otherwise as variously stated above.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-33. (canceled)
 34. A method of forming contact openings comprising:providing a bottom powered plasma chamber comprising a plasma generatingelectrode powerable at different first and second frequencies, the firstfrequency being lower than the second frequency; positioning a substrateover the electrode, the substrate comprising an insulative layercomprising silicon dioxide over conductive or semiconductive material,the insulative layer having an outermost portion and having an innermostportion proximate the conductive or semiconductive material, theoutermost portion having a thickness which is at least five times thatof the inner portion, the substrate comprising a patterned masking layerhaving openings therein for defining contact openings; and formingcontact openings through the insulative layer to the conductive orsemiconductive material using the patterned masking layer within thechamber, the forming comprising: removing the outermost portioneffective to expose the innermost portion; after exposing the innermostportion, plasma etching the innermost portion effective to expose theconductive or semiconductive material with a plasma generated with theelectrode from a first applied power at the first frequency and secondapplied power at the second frequency, a ratio of the first appliedpower to the second applied power being from greater than 0 to 0.25 orat least 6.0; and the removing comprising plasma etching with a plasmagenerated with the electrode from a third applied power at the firstfrequency and a fourth applied power at the second frequency, a ratio ofthe third applied power to the fourth applied power being from 0.26 to5.9 within the chamber, the forming of contact openings resulting inincreased field threshold voltage than would otherwise occur underidentical conditions except if plasma etching the innermost portion wereconducted using a ratio of the first applied power to the second appliedpower from 0.26 to 5.9.
 35. The method of claim 34 wherein the firstfrequency comprises 2 MHz and the second frequency comprises 27 MHz. 36.(canceled)
 37. The method of claim 34 wherein the material issemiconductive material and comprises polysilicon.
 38. The method ofclaim 34 wherein the material is conductive material and comprisescopper.
 39. The method of claim 34 wherein the patterned masking layercomprises photoresist.
 40. (canceled)
 41. The method of claim 40 claim34 wherein the thickness of the outermost portion is at least nine timesthe thickness of the innermost portion.
 42. The method of claim 34wherein the outermost portion is removed at a higher rate than theinnermost portion is plasma etched.
 43. The method of claim 34 whereinthe first applied power and the second applied power are each greaterthan 1000 watts.
 44. The method of claim 34 wherein a sum of the firstapplied power and the second applied power is at least 3000 watts. 45.The method of claim 34 wherein the first applied power is zero.
 46. Themethod of claim 34 wherein the first applied power is greater than zero.47-48. (canceled)
 49. The method of claim 34 wherein the ratio of thethird applied power to the fourth applied power is from 0.6 to 1.67. 50.The method of claim 34 wherein the third applied power and the fourthapplied power are each greater than 1000 watts.
 51. The method of claim34 wherein a sum of the third applied power and the fourth applied poweris at least 3000 watts.
 52. The method of claim 34 wherein the firstapplied power is equal to the third applied power and the second appliedpower is equal to the fourth applied power. 53-54. (canceled)